Grind the corn kernels into a paste. Add the semolina, rice flour and cooking soda to it. Mix well and set aside for few minutes. Heat little water in a vessel, add the grated jaggery and cardamom powder to it. Allow the jaggery to melt and cook until the syrup is sticky. Heat oil in deep frying vessel. Apply little oil or water on palm and take lemon size ball of corn batter, flatten them a little, make a hole in the middle. Deep fry them on low flame till crisp and golden color. When they turn to golden golden brown color, remove from the oil and put them into jaggery syrup. Soak the vadas in jaggery syrup for 5 minutes. Take the vadas out of the syrup and serve.